Systems and methods for material breakthrough

ABSTRACT

Methods may be performed to limit footing, pitch walking, and other alignment issues. The methods may include forming a treatment gas plasma within a processing region of a semiconductor processing chamber. The methods may further include directing effluents of the treatment gas plasma towards a semiconductor substrate within the processing region of the semiconductor processing chamber, and anisotropically modifying a surface of a first material on the semiconductor substrate with the effluents of the treatment gas plasma. The methods may also include passivating a surface of a second material on the semiconductor substrate with the effluents of the treatment gas plasma. The methods may further include forming a remote fluorine-containing plasma to produce fluorine-containing plasma effluents, and flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber. The methods may also include selectively removing the modified surface of the first material from the semiconductor substrate.

TECHNICAL FIELD

The present technology relates to semiconductor systems, processes, and equipment. More specifically, the present technology relates to systems and methods for selective etching.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers, or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process that etches one material faster than another facilitating, for example, a pattern transfer process. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits, and processes, etch processes have been developed with a selectivity towards a variety of materials.

Etch processes may be termed wet or dry based on the materials used in the process. A wet HF etch preferentially removes silicon oxide over other dielectrics and materials. However, wet processes may have difficulty penetrating some constrained trenches and also may sometimes deform the remaining material. Dry etches produced in local plasmas formed within the substrate processing region can penetrate more constrained trenches and exhibit less deformation of delicate remaining structures. However, local plasmas may damage the substrate and features formed on the substrate during subsequent process operations. Conventionally, feature damage, such as missing fin damage, is just accepted as part of the process.

Thus, there is a need for improved systems and methods that can be used to produce high quality devices and structures. These and other needs are addressed by the present technology.

SUMMARY

Exemplary etching methods may include forming a treatment gas plasma from a treatment gas precursor within a processing region of a semiconductor processing chamber. The etching methods may also include directing effluents of the treatment gas plasma towards a semiconductor substrate within the processing region of the semiconductor processing chamber. The etching methods may further include anisotropically modifying a surface of a first material on the semiconductor substrate with the effluents of the treatment gas plasma. The etching methods may also include passivating a surface of a second material on the semiconductor substrate with the effluents of the treatment gas plasma. The etching methods may also include forming a remote plasma from a fluorine-containing precursor to produce fluorine-containing plasma effluents. The etching methods may further include flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber. The etching methods may also include selectively removing the modified surface of the first material from the semiconductor substrate.

In some embodiments, the treatment gas precursor may include a mixture of a first precursor and a second precursor. In some embodiments, anisotropically modifying the surface of the first material may include anisotropically modifying the surface of the first material with plasma effluents of the first precursor. In some embodiments, the first precursor may include at least one of a nitrogen-containing precursor or a hydrogen-containing precursor. In some embodiments, passivating the surface of the second material may include passivating the surface of the second material with plasma effluents of the second precursor. In some embodiments, the second precursor may include at least one of an oxygen-containing precursor or a nitrogen-containing precursor. In some embodiments, the mixture may include less than or about 20% of the second precursor. In some embodiments, the first material may include a spacer material including an oxide material. In some embodiments, the second material may include a hardmask material including a nitride material.

The present technology may also include additional exemplary etching methods. The etching methods may include forming a treatment gas plasma within a processing region of a semiconductor processing chamber. The etching methods may also include modifying a surface of a first material on a semiconductor substrate within the processing region of the semiconductor processing chamber with effluents of the treatment gas plasma. The etching methods may further include modifying a surface of a second material on the semiconductor substrate with the effluents of the treatment gas plasma. The etching methods may also include forming a remote plasma from a fluorine-containing precursor to produce fluorine-containing plasma effluents. The etching methods may further include flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber. The etching methods may also include flowing water vapor to the processing region of the semiconductor processing chamber. The etching methods may further include selectively removing the modified surface of the first material from the semiconductor substrate.

In some embodiments, a temperature of the semiconductor substrate may be maintained between about 5° C. and about 35° C. In some embodiments, the fluorine-containing plasma effluents may be formed in a remote region of the semiconductor processing chamber fluidly coupled with, and physically separated from, the processing region of the semiconductor processing chamber. In some embodiments, the fluorine-containing plasma effluents may be produced by a capacitively-coupled plasma at a power level of less than or about 300 W. In some embodiments, the first material may include a spacer material including an oxide material. In some embodiments, the second material may include a hardmask material including a nitride material. In some embodiments, the etching methods may include a selectivity of at least 7:1 of the modified first material relative to the modified second material.

The present technology may further include additional exemplary etching methods. The etching methods may include forming a bias plasma from a carbon-containing precursor within a processing region of a semiconductor processing chamber to produce carbon-containing plasma effluents. The etching methods may also include selectively depositing a carbon-containing protective layer at a surface of a first material on a semiconductor substrate within the processing region of the semiconductor processing chamber with the carbon-containing plasma effluents. The etching methods may further include selectively removing a surface of a second material on the semiconductor substrate.

In some embodiments, the carbon-containing precursor may include methane. In some embodiments, the carbon-containing precursor further may include a dilution gas. In some embodiments, a ratio of a flow rate of the dilution gas to a flow rate of methane may be about 2:1. In some embodiments, the etching methods may also include depositing a carbon-containing protective layer at a surface of the second material. In some embodiments, a ratio of a thickness of the carbon-containing protective layer deposited at the surface of the first material to a thickness of the carbon-containing protective layer deposited at the surface of the second material may be at least about 3:1.

In some embodiments, the etching methods may also include forming a treatment gas plasma from a treatment gas precursor within the processing region of the semiconductor processing chamber. The etching methods may further include anisotropically modifying the surface of the second material with effluents of the treatment gas plasma. The etching methods may also include forming a remote plasma from a fluorine-containing precursor to produce fluorine-containing plasma effluents. The etching methods may further include flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber. The etching methods may also include selectively removing the modified surface of the first material from the semiconductor substrate with the fluorine-containing plasma effluents.

In some embodiments, the carbon-containing precursor may include a fluorine and carbon-containing precursor. In some embodiments, the carbon-containing precursor further may include a dilution gas. In some embodiments, a ratio of a flow rate of the dilution gas to a flow rate of the fluorine and carbon-containing precursor may be between about 20:1 and about 200:1.

Such technology may provide numerous benefits over conventional systems and techniques. For example, the technology may selectively remove spacer materials relative to hardmask materials, and footing issues may be prevented or limited. Additionally, given the directional or anisotropic etching provided by the technology, critical dimensions of spacers may be maintained and pitch walking and other alignment issues may be avoided. These and other embodiments, along with many of their advantages and features, are described in more detail in conjunction with the below description and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the disclosed technology may be realized by reference to the remaining portions of the specification and the drawings.

FIG. 1 shows a top plan view of an exemplary processing system according to the present technology.

FIG. 2 shows a schematic cross-sectional view of an exemplary processing chamber according to the present technology.

FIG. 3 shows selected operations in an etching method according to embodiments of the present technology.

FIGS. 4A-4G illustrate cross-sectional views of substrate materials on which selected operations are being performed according to embodiments of the present technology.

FIG. 5 shows selected operations in an etching method according to embodiments of the present technology.

FIGS. 6A and 6B illustrate cross-sectional views of substrate materials on which selected operations are being performed according to embodiments of the present technology.

FIGS. 7A-7C illustrate cross-sectional views of substrate materials on which selected operations are being performed according to embodiments of the present technology.

FIG. 8 shows selected operations in an etching method according to embodiments of the present technology.

FIGS. 9A-9C illustrate cross-sectional views of substrate materials on which selected operations are being performed according to embodiments of the present technology.

Several of the figures are included as schematics. It is to be understood that the figures are for illustrative purposes, and are not to be considered of scale unless specifically stated to be of scale. Additionally, as schematics, the figures are provided to aid comprehension and may not include all aspects or information compared to realistic representations, and may include superfluous or exaggerated material for illustrative purposes.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the letter.

DETAILED DESCRIPTION

The present technology includes systems and components for semiconductor processing of small pitch features. Multi-patterning techniques, such as Self-Aligned Double Patterning (SADP) or Self-Aligned Quadruple Patterning (SAQP), have been developed to enhance feature density for integrated circuits. Such multi-patterning techniques often involve forming multiple masks or barrier layers, such as mandrels, spacers, hardmask or etch stop layers, etc., and subsequently selectively removing or etching the masks or barrier layers at various processing steps. As line pitch continues to decrease, the dimensions, e.g., width or depths, of the masks or barrier layers employed are also reduced, which puts stringent requirements on mask losses, such as lateral spacer loss, loss of hardmask or etch stop layers. Conventional reactive ion etching processes have struggled to meet these requirements due to the sputtering component involved, which leads to faceted or more tapered spacer profiles at the top of the spacers, reduction or thinning of the spacer critical dimension, and loss of the hardmask or etch stop layers. Sputtering also creates footing along the spacer sidewalls. Mask losses and footing further lead to pitch walking and transferability issues. These issues become more prominent especially for sub-10 or sub-7 nm technology nodes with very small spacer critical dimensions.

The present technology takes advantage of a single chamber capable of both surface modification as well as etching capabilities to affect material quality, etch rates, and selectivity. Utilizing a bias plasma, directional or anisotropic modification of exposed areas may be achieved. The present technology also provides a variety of methods and etching chemistries that offers high etching selectivity of modified materials over unmodified materials. The present technology also provides methods and etching chemistries that improve etching selectivity of spacer materials over hardmask materials. As such, a flat top surface of etched spacers may be achieved, and spacer sidewall critical dimension may be maintained. Hardmask layer loss may also be prevented or minimized. The present technology reduces footing and prevents pitch walking and other alignment issues.

Although the remaining disclosure will routinely identify specific etching processes utilizing the disclosed technology, it will be readily understood that the systems and methods are equally applicable to deposition and cleaning processes as may occur in the described chambers. Accordingly, the technology should not be considered to be so limited as for use with etching processes alone.

FIG. 1 shows a top plan view of one embodiment of a processing system 100 of deposition, etching, baking, and curing chambers according to embodiments. The processing tool 100 depicted in FIG. 1 may contain a plurality of process chambers, 114A-D, a transfer chamber 110, a service chamber 116, an integrated metrology chamber 117, and a pair of load lock chambers 106A-B. The process chambers may include structures or components similar to those described in relation to FIG. 2, as well as additional processing chambers.

To transport substrates among the chambers, the transfer chamber 110 may contain a robotic transport mechanism 113. The transport mechanism 113 may have a pair of substrate transport blades 113A attached to the distal ends of extendible arms 113B, respectively. The blades 113A may be used for carrying individual substrates to and from the process chambers. In operation, one of the substrate transport blades such as blade 113A of the transport mechanism 113 may retrieve a substrate W from one of the load lock chambers such as chambers 106A-B and carry substrate W to a first stage of processing, for example, an etching process as described below in chambers 114A-D. If the chamber is occupied, the robot may wait until the processing is complete and then remove the processed substrate from the chamber with one blade 113A and may insert a new substrate with a second blade (not shown). Once the substrate is processed, it may then be moved to a second stage of processing. For each move, the transport mechanism 113 generally may have one blade carrying a substrate and one blade empty to execute a substrate exchange. The transport mechanism 113 may wait at each chamber until an exchange can be accomplished.

Once processing is complete within the process chambers, the transport mechanism 113 may move the substrate W from the last process chamber and transport the substrate W to a cassette within the load lock chambers 106A-B. From the load lock chambers 106A-B, the substrate may move into a factory interface 104. The factory interface 104 generally may operate to transfer substrates between pod loaders 105A-D in an atmospheric pressure clean environment and the load lock chambers 106A-B. The clean environment in factory interface 104 may be generally provided through air filtration processes, such as HEPA filtration, for example. Factory interface 104 may also include a substrate orienter/aligner (not shown) that may be used to properly align the substrates prior to processing. At least one substrate robot, such as robots 108A-B, may be positioned in factory interface 104 to transport substrates between various positions/locations within factory interface 104 and to other locations in communication therewith. Robots 108A-B may be configured to travel along a track system within enclosure 104 from a first end to a second end of the factory interface 104.

The processing system 100 may further include an integrated metrology chamber 117 to provide control signals, which may provide adaptive control over any of the processes being performed in the processing chambers. The integrated metrology chamber 117 may include any of a variety of metrological devices to measure various film properties, such as thickness, roughness, composition, and the metrology devices may further be capable of characterizing grating parameters such as critical dimensions, sidewall angle, and feature height under vacuum in an automated manner.

Turning now to FIG. 2 is shown a cross-sectional view of an exemplary process chamber system 200 according to the present technology. Chamber 200 may be used, for example, in one or more of the processing chamber sections 114 of the system 100 previously discussed Generally, the etch chamber 200 may include a first capacitively-coupled plasma source to implement an ion milling operation and a second capacitively-coupled plasma source to implement an etching operation and to implement an optional deposition operation. The chamber 200 may include grounded chamber walls 240 surrounding a chuck 250. In embodiments, the chuck 250 may be an electrostatic chuck that clamps the substrate 202 to a top surface of the chuck 250 during processing, though other clamping mechanisms as would be known may also be utilized. The chuck 250 may include an embedded heat exchanger coil 217. In the exemplary embodiment, the heat exchanger coil 217 includes one or more heat transfer fluid channels through which heat transfer fluid, such as an ethylene glycol/water mix, may be passed to control the temperature of the chuck 250 and ultimately the temperature of the substrate 202.

The chuck 250 may include a mesh 249 coupled to a high voltage DC supply 248 so that the mesh 249 may carry a DC bias potential to implement the electrostatic clamping of the substrate 202. The chuck 250 may be coupled with a first RF power source and in one such embodiment, the mesh 249 may be coupled with the first RF power source so that both the DC voltage offset and the RF voltage potentials are coupled across a thin dielectric layer on the top surface of the chuck 250. In the illustrative embodiment, the first RF power source may include a first and second RF generator 252, 253. The RF generators 252, 253 may operate at any industrially utilized frequency, however in the exemplary embodiment the RF generator 252 may operate at 60 MHz to provide advantageous directionality. Where a second RF generator 253 is also provided, the exemplary frequency may be 2 MHz.

With the chuck 250 to be RF powered, an RF return path may be provided by a first showerhead 225. The first showerhead 225 may be disposed above the chuck to distribute a first feed gas into a first chamber region 284 defined by the first showerhead 225 and the chamber wall 240. As such, the chuck 250 and the first showerhead 225 form a first RF coupled electrode pair to capacitively energize a first plasma 270 of a first feed gas within a first chamber region 284. A DC plasma bias, or RF bias, resulting from capacitive coupling of the RF powered chuck may generate an ion flux from the first plasma 270 to the substrate 202, e.g., He ions where the first feed gas is He, to provide an ion milling plasma. The first showerhead 225 may be grounded or alternately coupled with an RF source 228 having one or more generators operable at a frequency other than that of the chuck 250, e.g., 13.56 MHz or 60 MHz. In the illustrated embodiment the first showerhead 225 may be selectably coupled to ground or the RF source 228 through the relay 227 which may be automatically controlled during the etch process, for example by a controller (not shown). In disclosed embodiments, chamber 200 may not include showerhead 225 or dielectric spacer 220, and may instead include only baffle 215 and showerhead 210 described further below.

As further illustrated in the figure, the etch chamber 200 may include a pump stack capable of high throughput at low process pressures. In embodiments, at least one turbo molecular pump 265, 266 may be coupled with the first chamber region 284 through one or more gate valves 260 and disposed below the chuck 250, opposite the first showerhead 225. The turbo molecular pumps 265, 266 may be any commercially available pumps having suitable throughput and more particularly may be sized appropriately to maintain process pressures below or about 50 mTorr or below or about 20 mTorr at the desired flow rate of the first feed gas, e.g., 50 to 500 sccm of He where helium is the first feed gas. In the embodiment illustrated, the chuck 250 may form part of a pedestal which is centered between the two turbo pumps 265 and 266, however in alternate configurations chuck 250 may be on a pedestal cantilevered from the chamber wall 240 with a single turbo molecular pump having a center aligned with a center of the chuck 250.

Disposed above the first showerhead 225 may be a second showerhead 210. In one embodiment, during processing, the first feed gas source, for example, helium delivered from gas distribution system 290 may be coupled with a gas inlet 276, and the first feed gas flowed through a plurality of apertures 280 extending through second showerhead 210, into the second chamber region 281, and through a plurality of apertures 282 extending through the first showerhead 225 into the first chamber region 284. An additional flow distributor or baffle 215 having apertures 278 may further distribute a first feed gas flow 216 across the diameter of the etch chamber 200 through a distribution region 218. In an alternate embodiment, the first feed gas may be flowed directly into the first chamber region 284 via apertures 283 which are isolated from the second chamber region 281 as denoted by dashed line 223.

Chamber 200 may additionally be reconfigured from the state illustrated to perform an etching operation. A secondary electrode 205 may be disposed above the first showerhead 225 with a second chamber region 281 there between. The secondary electrode 205 may further form a lid or top plate of the etch chamber 200. The secondary electrode 205 and the first showerhead 225 may be electrically isolated by a dielectric ring 220 and form a second RF coupled electrode pair to capacitively discharge a second plasma 292 of a second feed gas within the second chamber region 281. Advantageously, the second plasma 292 may not provide a significant RF bias potential on the chuck 250. At least one electrode of the second RF coupled electrode pair may be coupled with an RF source for energizing an etching plasma. The secondary electrode 205 may be electrically coupled with the second showerhead 210. In an exemplary embodiment, the first showerhead 225 may be coupled with a ground plane or floating and may be coupled to ground through a relay 227 allowing the first showerhead 225 to also be powered by the RF power source 228 during the ion milling mode of operation. Where the first showerhead 225 is grounded, an RF power source 208, having one or more RF generators operating at 13.56 MHz or 60 MHz, for example, may be coupled with the secondary electrode 205 through a relay 207 which may allow the secondary electrode 205 to also be grounded during other operational modes, such as during an ion milling operation, although the secondary electrode 205 may also be left floating if the first showerhead 225 is powered.

A second feed gas source, such as nitrogen trifluoride, and a hydrogen source, such as ammonia, may be delivered from gas distribution system 290, and coupled with the gas inlet 276 such as via dashed line 224. In this mode, the second feed gas may flow through the second showerhead 210 and may be energized in the second chamber region 281. Reactive species may then pass into the first chamber region 284 to react with the substrate 202. As further illustrated, for embodiments where the first showerhead 225 is a multi-channel showerhead, one or more feed gases may be provided to react with the reactive species generated by the second plasma 292. In one such embodiment, a water source may be coupled with the plurality of apertures 283. Additional configurations may also be based on the general illustration provided, but with various components reconfigured. For example, flow distributor or baffle 215 may be a plate similar to the second showerhead 210, and may be positioned between the secondary electrode 205 and the second showerhead 210. As any of these plates may operate as an electrode in various configurations for producing plasma, one or more annular or other shaped spacer may be positioned between one or more of these components, similar to dielectric ring 220. Second showerhead 210 may also operate as an ion suppression plate in embodiments, and may be configured to reduce, limit, or suppress the flow of ionic species through the second showerhead 210, while still allowing the flow of neutral and radical species. One or more additional showerheads or distributors may be included in the chamber between first showerhead 225 and chuck 250. Such a showerhead may take the shape or structure of any of the distribution plates or structures previously described. Also, in embodiments a remote plasma unit (not shown) may be coupled with the gas inlet to provide plasma effluents to the chamber for use in various processes.

In an embodiment, the chuck 250 may be movable along the distance H2 in a direction normal to the first showerhead 225. The chuck 250 may be on an actuated mechanism surrounded by a bellows 255, or the like, to allow the chuck 250 to move closer to or farther from the first showerhead 225 as a means of controlling heat transfer between the chuck 250 and the first showerhead 225, which may be at an elevated temperature of 80° C.-150° C., or more. As such, an etch process may be implemented by moving the chuck 250 between first and second predetermined positions relative to the first showerhead 225. Alternatively, the chuck 250 may include a lifter 251 to elevate the substrate 202 off a top surface of the chuck 250 by distance H1 to control heating by the first showerhead 225 during the etch process. In other embodiments, where the etch process is performed at a fixed temperature such as about 90-110° C. for example, chuck displacement mechanisms may be avoided. A system controller (not shown) may alternately energize the first and second plasmas 270 and 292 during the etching process by alternately powering the first and second RF coupled electrode pairs automatically.

The chamber 200 may also be reconfigured to perform a deposition operation. A plasma 292 may be generated in the second chamber region 281 by an RF discharge which may be implemented in any of the manners described for the second plasma 292. Where the first showerhead 225 is powered to generate the plasma 292 during a deposition, the first showerhead 225 may be isolated from a grounded chamber wall 240 by a dielectric spacer 230 so as to be electrically floating relative to the chamber wall. In the exemplary embodiment, an oxidizer feed gas source, such as molecular oxygen, may be delivered from gas distribution system 290, and coupled with the gas inlet 276. In embodiments where the first showerhead 225 is a multi-channel showerhead, any silicon-containing precursor, such as OMCTS for example, may be delivered from gas distribution system 290, and directed into the first chamber region 284 to react with reactive species passing through the first showerhead 225 from the plasma 292. Alternatively the silicon-containing precursor may also be flowed through the gas inlet 276 along with the oxidizer. Chamber 200 is included as a general chamber configuration that may be utilized for various operations discussed in reference to the present technology. The chamber is not to be considered limiting to the technology, but instead to aid in understanding of the processes described. Several other chambers known in the art or being developed may be utilized with the present technology including any chamber produced by Applied Materials Inc. of Santa Clara, Calif., or any chamber that may perform the techniques described in more detail below.

FIG. 3 illustrates exemplary operations of a method 300 that may be performed, for example, in the chamber 200 as previously described. Prior to the first operation of the method, a substrate may be processed in one or more ways before being placed within a processing region of a chamber in which method 300 may be performed. For example, films or layers may be deposited, grown, or otherwise formed on the substrates, and masks for patterning the films or layers may be formed to produce features. FIG. 4A illustrates a portion of such a processed structure 400, which may be produced during a multi-patterning process. The processed structure 400 may be further developed in producing, for example, fin-based structures, or any other semiconductor structures, using method 300, the operations of which will be described in conjunction with the schematic illustration of FIGS. 4A-4G.

With reference to FIG. 4A, the processed structure 400 may include a hardmask or etch stop layer 405, one or more patterned structures or mandrels 410, and a spacer material layer 415 overlaying the hardmask layer 405 and the mandrels 410. Although two mandrels 410 are shown in FIG. 4A, the processed structure 400 may include more or fewer mandrels 410. The mandrels 410 may include a semiconductor material, such as silicon. In some embodiments, the mandrels 410 may be or may include polysilicon mandrels 410. The spacer material layer 415 may include an oxide, such as silicon oxide or other oxide that may be used or useful in semiconductor processes. The hardmask layer 405 may include a nitride, such as silicon nitride, titanium nitride, or other nitride or hardmask materials that may resist etching during the etching process for the spacer material 415 and the mandrels 410 as discussed below. Although not shown, the processed structure 400 may include additional layers below the hardmask layer 405 overlaying a substrate. In some embodiments, the processed structure 400 may be produced in the same processing chamber as the processing chamber in which method 300 may be performed, or may be produced in a different processing chamber and then transferred to the processing chamber in which method 300 may be performed.

Once the processed structure 400 may be positioned within a processing region of a semiconductor processing chamber, such as the first chamber region 284 of the processing chamber 200 discussed above with reference to FIG. 2, method 300 may be initiated by forming a treatment gas plasma formed from a treatment gas precursor within the processing region at operation 305. Such a plasma is similarly understood to be a wafer-level plasma. The plasma of the treatment gas precursor may be a bias plasma, providing directional flow of the plasma effluents 420 of the treatment gas precursor towards the processed structure 400 at operation 310, as illustrated in FIG. 4B. At operation 315, the plasma effluents 420 of the treatment gas precursor may modify the exposed region of the processed structure 400, such as the spacer material layer 415. Given the directional flow of the plasma effluents 420, modification may be anisotropic. Modified layers 425 a may be formed at the top surface regions of the spacer material layer 415, and modified layers 425 b may also be formed at the bottom surface regions of the spacer material layer 415. Modification may not occur along sidewalls of the spacer material layer 415.

A remote plasma may be formed at operation 320 to produce plasma effluents, and the remote plasma may include or be composed of a halogen-containing precursor. At operation 325, the plasma effluents may be flowed through the processing chamber to the processing region of the processing chamber where the processed structure 400 may be housed. In embodiments, the plasma utilized in operation 320 may also be formed at the wafer level, but ions of a remote plasma may be filtered out by a showerhead or other structure through which the effluents may be flowed at operation 325, thereby reducing a sputtering component at the wafer. Upon contacting the modified layers 425, at operation 330, the plasma effluents may remove the modified layers 425 of the spacer material layer 415. The plasma effluents may have an etching selectivity of the modified layers 425 to the unmodified portion of the spacer material layer 415. As such, at operation 330, the plasma effluents may remove the modified layers 425 but may have very limited, or substantially no removal of the exposed, unmodified sidewalls of the spacer material layer 415 or the subsequently exposed, unmodified portion of the spacer material layer 415, resulting in the processed structure 400 as shown in FIG. 4C. Because only the depth dimension of the spacer material layer 415 may be reduced through performance of method 300, the width dimension of the sidewalls of the spacer material layer 415 may be substantially maintained, and critical dimension uniformity of the spacers may be maintained.

The treatment gas precursors involved in operations 305-315 for modifying the spacer material layer 415 may include one or more inert gas materials, such as helium, neon, argon, etc. The treatment gas precursors may also include precursors that may have limited chemical activity or may be unreactive with the spacer material layer 415, such as oxygen-containing precursors and/or hydrogen-containing precursors. The oxygen-containing precursors may include diatomic oxygen, carbon oxide, such as carbon dioxide, nitrogen oxide, such as dinitrogen monoxide, or other precursors including oxygen. The hydrogen-containing precursors may include diatomic hydrogen, ammonia, or other precursors including hydrogen.

The bias plasma involved in operations 305-315 for providing directional flow of the plasma effluents 420 towards the surface of the spacer material layer 415 of the processed structure 400 may be a low-level plasma to limit sputtering of the exposed regions of the processed structure 400 and to control the amount or depth of surface modification. In some embodiments, the plasma power may be less than or about 500 W, less than or about 450 W, less than or about 400 W, less than or about 350 W, less than or about 300 W, less than or about 250 W, less than or about 200 W, less than or about 150 W, less than or about 100 W, less than or about 75 W, less than or about 50 W, less than or about 25 W, less than or about 20 W, less than or about 15 W, less than or about 10 W, less than or about 5 W, or less, depending on the treatment gas precursor utilized and the desired depth of the modification. For example, when the plasma effluents 420 of the treatment gas precursors may include relatively small or light materials, such as hydrogen ions, a higher bias power, such as about 40 W or more, may be utilized to achieve a desired depth of modification. To achieve a similar depth of modification, when the plasma effluents 420 of the treatment gas precursors may include relatively large or heavy material, such as argon ions, a lower bias power, such as 30 W or less, may be utilized to direct the flow of argon ions.

Depending on the treatment gas precursors and the bias plasma power employed, the depth of the modified layers 425 as shown in FIG. 4B may be about 1 nm, about 2 nm, about 3 nm, about 4 nm, or more, which in turn may lead to about 1 nm, about 2 nm, about 3 nm, about 4 nm, or more material removal at the removal operation 330. Depending on the particular application, operations 305-330 may be repeated in cycles to remove the spacer material layer 415 until the mandrels 410 and/or the hardmask layer 405 underlying the spacer material layer 415 may be exposed. In some embodiments, operations 305-330 may be performed for 1 cycle, 2 cycles, 3 cycles, 4 cycles, 5 cycles, or more in order to expose the mandrel 410 and/or the hardmask layer 405 underneath the spacer material layer 415. In some embodiments, during each cycle, the modification operation 315 may last less than or about 80 seconds, less than or about 70 seconds, less than or about 60 seconds, less than or about 50 seconds, less than or about 40 seconds, less than or about 30 seconds, less than or about 20 seconds, less than or about 10 seconds, less than or about 5 seconds, or less in embodiments, depending on the desired thickness of the spacer material layer 415 to be modified and thus removed in the subsequent removal operation 330.

The pressure within the processing chamber may be controlled during the modification operation 315 as well. For example, while forming the bias plasma and performing the modification operation 315, the pressure within the processing region may be maintained below or about 1 Torr. In some embodiments, the pressure within the processing chamber may be maintained below or about 700 mTorr, below or about 600 mTorr, below or about 500 mTorr, below or about 400 mTorr, below or about 300 mTorr, below or about 250 mTorr, below or about 200 mTorr, below or about 150 mTorr, below or about 100 mTorr, below or about 80 mTorr, below or about 60 mTorr, below or about 40 mTorr, below or about 20 mTorr, below or about 10 mTorr, below or about 5 mTorr, below or about 3 mTorr, or lower. Relatively lower pressures within the processing region may be desired so as to increase the mean free path of the particles of plasma effluents 420 and to increase the directionality of the modification operation 315.

The plasma involved in operations 320-330 may be formed remotely from the processing region of the processing chamber. For example, the plasma may be formed in a region of the processing chamber that is fluidly isolated from the processing region of the processing chamber. Thus, the remote plasma region may be physically separated from the processing region, while being fluidly coupled with the processing region. For example, in the exemplary chamber of FIG. 2, the remote plasma may be generated in region 281, which is separated from the processing region 284 by the showerhead 225. Additionally, the remote plasma may be formed in a remote plasma unit, such as an RPS unit that is separate from the chamber, but fluidly coupled with the chamber to deliver plasma effluents into the chamber, such as through a lid, top plate, or showerhead.

The remote plasma power involved in operations 320-330 may be greater than the wafer-level bias plasma power involved in operations 305-315 because ions or charged particulars may be removed from the plasma effluents by the showerhead as the plasma effluents travel towards the processing region where the processed structure 400 may be housed. In some embodiments, the remote plasma power involved in operations 320-330 may be between about 50 W and about 500 W. In some embodiments, the remote plasma power may be less than or about 450 W, less than or about 400 W, less than or about 350 W, less than or about 300 W, less than or about 250 W, less than or about 200 W, less than or about 150 W, less than or about 100 W, less than or about 75 W, less than or about 50 W, or less.

The remote plasma involved in operations 320-330 may be formed from one or more precursors including a halogen-containing precursor, such as including a fluorine-containing precursor, for example. The fluorine-containing precursor may include one or more materials including NF₃, HF, F₂, CF₄, CHF₃, C₂F₆, C₃F₆, BrF₃, ClF₃, SF₆, or additional fluorine-substituted hydrocarbons, or fluorine-containing materials. The fluorine-containing precursor may be flowed into the remote plasma region to generate plasma effluents, such as fluorine-containing plasma effluents.

A source of hydrogen may also be incorporated as an etchant precursor, and may include hydrogen, ammonia, or any other incompletely substituted hydrocarbon, or other hydrogen-containing material. The source of hydrogen, such as ammonia, for example, may be delivered with the fluorine-containing precursor into the remote plasma region during plasma formation, and thus the plasma effluents may also include hydrogen-containing plasma effluents. The source of hydrogen may also bypass the remote plasma region and be delivered into the processing region where it may be radicalized through interaction with the fluorine-containing plasma effluents. In either scenario, the plasma effluents may be delivered to the processing region of the semiconductor processing chamber where they may contact or interact with the modified layer 425 of the spacer material layer 415 of the processed structure 400. Helium or other carrier gas may also be included for uniform distribution of the plasma effluents when flowed through the showerhead into the processing region.

As discussed above, only a thin surface layer of the spacer material layer 415 may be modified during the modification process, and the depth of the modified layers 425 may be between only a few nanometers or less, the amount of fluorine-containing precursor flowed during the removal process may be controlled at relatively low level. In some embodiments, the flow rate of the fluorine-containing precursor may be maintained below or about 30 sccm, below or about 25 sccm, below or about 20 sccm, below or about 15 sccm, below or about 10 sccm, below or about 5 sccm, or lower. The flow rate of the hydrogen-containing precursor and/or the carrier gases may be maintained above or about 10 sccm, above or about 50 sccm, above or about 100 sccm, above or about 150 sccm, above or about 200 sccm above or about 250 sccm, above or about 300 sccm, above or about 350 sccm, above or about 400 sccm, above or about 500 sccm, above or about 600 sccm, above or about 700 sccm, above or about 800 sccm, above or about 900 sccm, above or about 1,000 sccm, or greater. A relatively low ratio of the fluorine-containing precursor to hydrogen-containing precursor and/or carrier gases may facilitate removing only the modified layers 425 and thus improve the selectivity of the modified layer 425 over the unmodified spacer material layer 415. In some embodiments, operations 305-330 of method 300 may achieve a selectivity of modified portions of the spacer material layer 415 to unmodified portions of the spacer material layer 415 greater than or about 10:1, greater than or about 20:1, greater than or about 40:1, greater than or about 100:1, greater than or about 1,000:1, or up to about 1:0 at which point the modified portion of the spacer material layer 415 may etch, but the unmodified portion of the spacer material layer 415 may not etch.

During the operations 320-330, a temperature of the processed structure 400 or the processing region may be maintained above or about 50° C., above or about 60° C., above or about 70° C., above or about 80° C., above or about 90° C., above or about 100° C., above or about 110° C., above or about 120° C., above or about 130° C., above or about 140° C., or above or about 150° C., or higher. In some embodiments, the temperature of the processed structure 400 or the processing region may be maintained between about 80° C. and about 110° C. to selectively etch the modified layers 425 while the unmodified portions of the spacer material layer 415 may not be etched with the removal process. Because the modification process involving operations 305-315 may be less sensitive to the temperature of the processed structure 400 and/or the processing region of the chamber, temperature of the processed structure 400 and/or the processing region may be maintained at a temperature the same as or similar to that maintained during the removal process involving operations 320-330.

As discussed above, depending on particular applications, operations 305-330 may be repeated in cycles to remove the spacer material layer 415 until the mandrels 410 and/or the hardmask layer 405 underlying the spacer material layer 415 may be exposed. Although the spacer material layer 415 may be deposited as a blanket layer, the thickness of the portion of the spacer material layer 415 near a top region of the mandrels 410 and the thickness of the portion of the spacer material layer 415 near a bottom region of the mandrels 410, such as the portion overlaying the hardmask layer 405 between the mandrels 410, may vary. For example, the portion of the spacer material layer 415 near the top region of the mandrels 410 may have a greater thickness than that of the portion of the spacer material layer 415 near the bottom region of the mandrels 410 overlaying portions of the hardmask layer 405, or vice versa. As such, after performing operations 305-330 for multiple cycles, the hardmask layer 405, or portions thereof, may be exposed, whereas the mandrels 410 may not be completely exposed, such as shown in FIG. 4D. Although FIG. 4D illustrates the scenario where the remaining spacer material layer 415 overlaying the top region of the mandrels 410 may include a greater thickness than the remaining spacer material layer 415 that may overlay portions of hardmask layer 405, in some embodiments, more of the spacer material layer 415 overlaying portions of the hardmask layer 405 may remain than the spacer material layer 415 overlaying the top region of the mandrels 410.

To ensure complete removal of the portions of the spacer material layer 415 overlaying the mandrels 410 and to expose the mandrels 410, method 300 may further include an over etch process, which may include operations 335-360 to be discussed below, by increasing the operation time of the last cycle by about 5%, about 10%, about 15%, about 20%, or more, depending on the particular applications. During over etch, the exposed portions of the hardmask layer 405, as well as the portions of the hardmask layer 405 underneath only very thin portions of the spacer material layer 415, may also be modified. If the same treatment gas precursors as those utilized in operations 305-315 may be used for the over etch process, the modified portions of the hardmask layer 405 may also be removed in the subsequent removal operation, which may lead to recesses formed in the hardmask layer 405 between the sidewalls of the spacer material layer 415 and overall unevenness of the hardmask layer 405. Such loss of the hardmask layer 405 may be undesirable in many instances. To avoid unwanted removal of the hardmask layer 405, alternative treatment gas precursors may be utilized during the over etch process.

At operation 335, a treatment gas plasma from a diluted treatment gas precursor within the processing region may be formed. Similar to the plasma formed at operation 305, the diluted treatment gas plasma may also be a wafer-level, bias plasma, providing directional flow of the plasma effluents 430 of the treatment gas precursor towards the processed structure 400 at operation 340, as illustrated in FIG. 4E. Given the directional flow of the plasma effluents 430, at operation 345, the plasma effluents 430 of the diluted treatment gas precursor may anisotropically modify the exposed region of the processed structure 400. The exposed region of the processed structure 400 that may be modified by the plasma effluents 430 may include the remaining spacer material layer 415 near the top region of the mandrels 410, the remaining spacer material layer 415 near the bottom region of the mandrels 410 and overlaying portions of the hardmask layer 405, and partially exposed portions of the hardmask layer 405. Because the remaining spacer material layer 415 overlaying portions of the hardmask layer 405 may be very thin, surface portions of the hardmask layer 405 underneath the spacer material layer 415, although not exposed, may also be modified during operation 345. During operations 335-345, operational conditions, such as pressure, temperature, bias plasma power, etc., may be maintained at similar levels to those maintained during operation 305-315.

The treatment gas precursors involved in operations 335-345 may be a mixture of two or more gases. At least one of the treatment gas precursors may modify the spacer material layer 415 to be removed, and at least one of the treatment gas precursors may be a dilution gas that may modify or passivate the hardmask layer 405 to limit subsequent removal of the hardmask layer 405. Without intending to be bound by any particular theory, the dilution gas may passivate the hardmask layer 405 through penetration into the hardmask layer 405, and may form a more densely packed surface layer of the hardmask layer 405, which may not be easily removed in the subsequent removal operation, thereby preserving the hardmask layer 405. The treatment gas precursor that may modify the spacer material layer 415 may include nitrogen-containing and/or hydrogen-containing precursors, such as diatomic nitrogen, diatomic hydrogen, and ammonia. The dilution gas may include oxygen-containing precursors, such as diatomic oxygen, or nitrogen-containing precursors, such as diatomic nitrogen. In some embodiments, the treatment gas precursors may include nitrogen gas diluted with oxygen gas, ammonia diluted with nitrogen gas, or hydrogen gas diluted with oxygen gas or nitrogen gas. The dilution gas may constitute less than or about 50%, less than or about 40%, less than or about 30%, less than or about 20%, less than or about 10%, less than or about 5%, or less of the diluted treatment gas precursors.

To remove the modified spacer material layer 415, operations 350-360, similar to operations 320-330, may be performed. At operation 350, a remote plasma may be formed to produce plasma effluents, and the remote plasma may be formed from a halogen-containing precursor, such as a fluorine-containing precursor, similar to the remote plasma formed at operation 320. The plasma effluents may be flowed through the processing chamber to the processing region towards the processed structure 400 at operation 355. Upon contacting the modified spacer material layer 415, at operation 360, the plasma effluents may remove the modified spacer material layer 415 but may remove little of the hardmask layer 405, resulting in the processed structure 400 as shown in FIG. 4F. Although the diluted treatment gas precursors are described herein in the process of over etch, the diluted treatment gas precursors may also be utilized during operations 305-315 because the same or even greater selectivity of the modified spacer material layer 415 by the diluted treatment gas precursors to the unmodified spacer material layer 415 may be achieved using the remote plasma effluents utilized in operations 320-330.

Once the portions of the spacer material layer 415 overlaying the mandrels 410 may be removed and the mandrels 410 may be exposed, method 300 may proceed to operation 365 to remove the mandrels 410. The mandrels 410 may be polysilicon mandrels, and may be removed using a fluorine-containing precursor. For example, a remote plasma of a fluorine-containing precursor, such as nitrogen trifluoride, may be formed and flowed to the processing region together with hydrogen and carrier gases to remove the polysilicon mandrels 410, resulting in the structure shown in FIG. 4G.

With reference to FIGS. 5, 6A and 6B, another exemplary method 500 for improving etching selectivity of the spacer material layer 415 over the hardmask layer 405 will be described. As shown in FIG. 5, method 500 may include operations 505-530 for processing a processed structure, such the processed structure 400 as shown in FIG. 4A. Specifically, method 500 may include a modification process including operations 505-515, same as or similar to operations 305-315 of method 300, and an etching process including operations 520-530, same as or similar to operations 320-350 of method 300 to selectively remove modified spacer material layer 415 over unmodified spacer material layer 415. Operations 505-530 may be performed in multiple cycles until a very thin layer of the spacer material layer 415 may remain overlaying the mandrels 410 and/or portions of the hardmask layer 405, resulting in the structure similar to that shown in FIG. 4D. Then, method 500 may proceed to an over etch process.

Different from method 300 where diluted treatment gas precursors may be used during the over etch process for modifying the exposed surfaces of the processed structure 400, method 500 may utilize treatment gas precursors that may be the same as or similar to those used during operations 505-515 or operations 305-315. Accordingly, during the over etch process, method 500 may include operations 535-545 that may be the same as or similar to operations 505-515 and/or operations 305-315. Specifically, at operation 535, a bias plasma of any treatment gas precursor as discussed above with reference to operations 305-315 of method 300 may be formed at wafer level in the processing region. At operation 540, the plasma effluents 610, which may be the same as or similar to the plasma effluents 420 described above with reference to FIG. 4B, may be directed by the plasma bias towards the processed structure 400, as illustrated in FIG. 6A. At operation 545, the plasma effluents 610 may modify the exposed region of the processed structure 400, such as the remaining spacer material layer 415 as well as exposed portions of the hardmask layer 405 and portions of the hardmask layer 405 underlying the very thin remaining spacer material layer 415, as shown in FIG. 6A.

As mentioned above, the same etching precursors as those utilized during operations 520-530 or operations 320-330 may also remove modified portions of the hardmask layer 405. To avoid undesirable loss or removal of the hardmask layer 405 during the over etch process, method 500 may utilize etching precursors different from those utilized during operations 520-530 or operations 320-330. Specifically, method 500 may include, at operation 550, forming a remote plasma from a halogen-containing precursor, such as a fluorine-containing precursor, to produce plasma effluents. At operation 555, the plasma effluents may be flowed through the processing chamber to the processing region of the processing chamber where the processed structure 400 may be housed. At operation 560, water vapor may be flowed into the processing region and combined with the plasma effluents. In some embodiments, the water vapor may not be passed through the remote plasma region and may be excited by interaction with the plasma effluents.

At operation 565, the plasma effluents combined with water vapor may selectively remove the modified spacer material layer 415 but may remove little or none of the modified hardmask layer 405, resulting in the structure shown in FIG. 6B. Without intending to be bound by any particular theory, the selective etching may be achieved due to the different wetting properties water may exhibit at the modified spacer material layer 415 and the modified hardmask layer 405. The water vapor may be adsorbed at the modified spacer material layer 415 whereas the adsorption of water vapor at the modified hardmask layer 405 may be limited. The adsorbed water vapor at the modified spacer material layer 415 may act as an catalyst for the fluorine-containing plasma effluents to interact with and consequently remove the modified spacer material layer 415. Due to the lack of water catalyst at the modified hardmask layer 405, the removal of the modified hardmask layer 405 may be limited or substantially prevented. An etching selectivity of the modified spacer material layer 415 over the modified hardmask layer 405 of at least above or about 5:1, above or about 6:1, above or about 7:1, above or about 8:1, above or about 9:1, above or about 10:1, or greater may be achieved. In contrast, without modifying the etching precursors utilized during the over etch operations 550-565, a selectivity of the modified spacer material layer 415 to the modified hardmask layer 405 may be about 2:1 or less.

The plasma involved in operation 550 may be formed remotely from the processing region of the processing chamber. For example, the plasma may be formed in a region of the processing chamber that is fluidly isolated from the processing region of the processing chamber. Thus, the remote plasma region may be physically separated from the processing region, while being fluidly coupled with the processing region. For example, in the exemplary chamber of FIG. 2, the remote plasma may be generated in region 281, which is separated from the processing region 284 by the showerhead 225. Additionally, the remote plasma may be formed in a remote plasma unit, such as an RPS unit that is separate from the chamber, but fluidly coupled with the chamber to deliver plasma effluents into the chamber, such as through a lid, top plate, or showerhead. The plasma power may be between about 50 W to 500 W. In some embodiments, the plasma power may be less than or about 500 W, less than or about 450 W, less than or about 400 W, less than or about 350 W, less than or about 300 W, less than or about 250 W, less than or about 200 W, less than or about 150 W, less than or about 100 W, or less.

The fluorine-containing precursor for forming the remote plasma may include one or more materials including NF₃, HF, F₂, CF₄, CHF₃, C₂F₆, C₃F₆, or additional fluorine-substituted hydrocarbons, or fluorine-containing materials. The fluorine-containing precursor may be flowed at a flow rate below or about 50 sccm, below or about 40 sccm, below or about 30 sccm, below or about 20 sccm, below or about 10 sccm, below or about 5 sccm, or lower. Given the relatively low flow rate of the fluorine-containing precursor, a dilution gas may be flowed together with the fluorine-containing precursor to ensure uniform distribution of the fluorine-containing plasma effluents towards the processed structure 400. The dilution gas may include helium or other inert gases that may be flowed at a flow rate above or about 500 sccm, above or about 1,000 sccm, above or about 1,500 sccm, above or about 2,000 sccm, above or about 2,500 sccm, above or about 3,000 sccm, above or about 3,500 sccm, above or about 4,000 sccm, above or about 4,500 sccm, above or about 5,000 sccm, or higher. In some embodiments, the ratio of the flow rate of the dilution gas to the flow rate of the fluorine-containing precursor may be 50:1, 100:1, 150:1, 200:1, 250:1, or greater. In some embodiments, the flow rate of the fluorine-containing precursor may be about 20 sccm, and the flow rate of the dilution gas, such as helium, may be about 3,500 sccm.

The delivery of water vapor may be achieved using a mass flow meter (MFM), mass flow controller (MFC), an injection valve, or by any suitable water vapor generators. In some embodiments, the water vapor may be carried by a carrier gas, such as helium or other inert gas, flowed through a bubbler. The carrier gas may be flowed at a flow rate of above or about 400 sccm, above or about 600 sccm, above or about 800 sccm, above or about 1,000 sccm, above or about 1,500 sccm, above or about 2,000 sccm, or greater. The water vapor delivered may be above or about 400 mgm, above or about 600 mgm, above or about 800 mgm, above or about 1,000 mgm, above or about 1,500 mgm, above or about 2,000 mgm, or greater. In some embodiments, 1,000 mgm water vapor may be delivered by a carrier gas of helium that may be flowed at a flow rate of 1,000 sccm.

To facilitate the adsorption of water vapor at the modified spacer material layer 415, the temperature at the substrate level or in the processing region may be maintained between about 0° C. and about 50° C., such as between about 5° C. and about 35° C. The temperature may be maintained below or about 40° C., below or about 35° C., below or about 30° C., below or about 25° C., below or about 20° C., below or about 15° C., below or about 10° C., below or about 5° C., or lower. The temperature may be maintained through a heat exchanger, such as the heat exchanger coil 217 embedded in the chuck 250 shown in FIG. 2. The heat exchanger coil may include one or more heat transfer fluid channels through which heat transfer fluid, such as an ethylene glycol/water mix, may be passed to control the temperature of the chuck and ultimately the temperature of the processed structure 400.

It is observed that the fluorine-containing effluents combined with water vapor, as discussed above with reference to operations 550-565, may not only have high etching selectivity of modified spacer material layer 415 over the hardmask layer 405, but the fluorine-containing effluents combined with water vapor may also have high etching selectivity of modified spacer material layer 415 over unmodified spacer material layer 415. The selectivity of the modified spacer material layer 415 over the unmodified spacer material layer 415 may be at least above or about 5:1, above or about 6:1, above or about 7:1, above or about 8:1, above or about 9:1, above or about 10:1, above or about 15:1, above or about 20:1, or greater. Accordingly, to produce the processed structure 400 shown in FIG. 4F or FIG. 6B without removing the hardmask layer 405, operations 505-530 of method 500 may be omitted. Rather, operations 535-560 may be performed in cycles until the mandrels 410 may be completely exposed. As discussed above, the temperature at the substrate level or in the processing region during operations 550-565 may be maintained within a lower range, such as between about 0° C. and about 50° C., as compared to that maintained during operations 520-530 or operations 320-330, such as between about 50° C. to about 140° C. Performing operations 535-560 only in cycles for the entire process may eliminate the need to adjust the operating temperature for the over etch process.

With reference to FIGS. 7A-7C, another exemplary method for improving etching selectivity of the spacer material layer 415 over the hardmask layer 405 will be described. Different from method 300 where diluted treatment gas precursors may be used for the over etch process or method 500 where different etching precursors may be used for the over etch process, the method as illustrated in FIGS. 7A-7C may involve selective deposition or coating of a protective layer over any exposed hardmask layer 405 prior to the over etch process. Specifically, the processed structure 400 shown in FIG. 4A may be processed using either operations 305-330 of method 300 or operations 505-530 of method 500 such that a very thin layer of the spacer material layer 415 may remain overlaying the mandrels 410 and/or portions of the hardmask layer 405, resulting in the structure similar to that shown in FIG. 4D.

Prior to the over etch process, selective coating of a protective layer at the hardmask layer 405 may be performed by forming a bias plasma from carbon-containing precursors in the processing region where the processed structure 400 may be housed. The plasma bias may direct the flow of carbon-containing plasma effluents 710 towards the processed structure 400, and a protective layer 720 that may be composed of carbon may be selectively deposited at the exposed regions of the hardmask layer 405. Due to the reaction that may happen between the carbon from the carbon-containing plasma effluents and the oxygen in the spacer material layer 415, deposition of the protective layer 730 at the spacer material layer 415 may be limited, resulting in the processed structure 400 shown in FIG. 7A. Depending on the operating conditions, the ratio of the thickness of the protective layer 720 that may be deposited at the exposed regions of the hardmask layer 405 to the thickness of the protective layer 730 that may be deposited at the spacer material layer 415 may be at least about 2:1, about 3:1, about 4:1, about 5:1, or greater.

The bias plasma power may be between about 10 W to 150 W. In some embodiments, the plasma power may be below or about 150 W, below or about 100 W, below or about 80 W, below or about 60 W, below or about 50 W, below or about 40 W, below or about 30 W, below or about 20 W, or less. Because the directional deposition of the carbon-containing protective layer may involve a form of bombardment, a relatively low bias plasma power, such as below or about 50 W, may be utilized so as to prevent or limit surface modification of the hardmask layer 405 by the other components in the plasma effluents, thereby preventing or limiting any subsequent removal of the hardmask layer 405.

The carbon-containing precursors may include hydrocarbon precursors, such as methyl-containing precursors in embodiments. For example, the carbon-containing precursors may include methane (CH₄). In some embodiments, the carbon-containing precursors may be flowed together with carrier or dilution gases including inert gases, such as helium or other noble gases, nitrogen gas, or hydrogen-containing gases, such as ammonia. The ratio of the flow rate of the dilution gases to the flow rate of the carbon-containing precursors may be about 1.5:1, about 2:1, about 2.5:1, about 3:1, about 4:1, or greater. For example, the flow rate of the carbon-containing precursors may be about 25 sccm, and the flow rate of the dilution gases, such as helium, nitrogen, or ammonia, may be about 50 sccm. In some embodiments, the carbon-containing precursors may be flowed without any carrier or dilution gases. The flow rate of the carbon-containing precursors may be between about 5 sccm and about 100 sccm, between about 15 sccm and about 75 sccm, or between about 25 sccm and about 50 sccm in various embodiments.

A relatively low pressure of the processing region may be maintained so as to increase the directionality of the deposition of the protection film. In some embodiments, the pressure may be maintained below or about 200 mTorr, below or about 150 mTorr, below or about 100 mTorr, below or about 50 mTorr, below or about 25 mTorr, below or about 20 mTorr, below or about 15 mTorr, below or about 10 mTorr, below or about 5 mTorr, or lower. The temperature of the processed structure 400 or the processing region may be maintained above or about 50° C., above or about 60° C., above or about 70° C., above or about 80° C., above or about 90° C., above or about 100° C., above or about 110° C., above or about 120° C., above or about 130° C., above or about 140° C., or above or about 150° C. In some embodiments, the temperature of the processed structure 400 or the processing region may be maintained between about 80° C. and about 110° C., such as 90° C.

Depending on the particular application, the selective deposition of the carbon protective layer may last less than or about 80 seconds, less than or about 70 seconds, less than or about 60 seconds, less than or about 50 seconds, less than or about 40 seconds, less than or about 30 seconds, less than or about 20 seconds, less than or about 10 seconds, less than or about 5 seconds, or less in embodiments. In some embodiments, the thickness of the carbon protective layer 720 deposited over any exposed regions of the hardmask layer 405 may be less than or about 5 nm, less than or about 4 nm, less than or about 3 nm, less than or about 2 nm, less than or about 1 nm, or less, which may provide sufficient protection to limit or prevent removal of the hardmask layer 405.

By utilizing the protective coating to limit or prevent undesirable removal of the hardmask layer 405, the same treatment gas precursors or the same etching precursors may be utilized throughout the entire method when processing the processed structure 400 shown in FIG. 4A into the processed structure 400 shown in FIG. 4F or FIG. 6B. For example, the treatment gas precursors involved in operations 305-315 or operations 505-515 may be utilized during the over etch process. Due to the relatively thick carbon protective film 720 being deposited, the treatment gas precursors may not modify any hardmask layer 405, whereas the treatment gas precursors may still modify the spacer material layer 415 to form a modified layer 740 of the spacer material layer 415, as shown in FIG. 7B, because the spacer material layer 415 may be covered only by the very thin or substantially none carbon deposition 730. Accordingly, during subsequent etching process, such as operations 320-330 or operations 520-530, the modified layer 740 of the spacer material layer 415 may be removed, whereas no or little removal of the hardmask layer 405 may occur. With a subsequent carbon removal operation, the processed structure 400 shown in FIG. 7C may be obtained. In some embodiments, if desired, the diluted treatment gas precursors involved in operations 335-345 of method 300 and the etching precursors involved in operations 550-565 of method 500 for the over etch process may be utilized in conjunction with the protective coating or deposition to further protect the hardmask layer 405 from being removed.

With reference to FIGS. 8 and 9A-9C, another exemplary method 800 for improving etching selectivity of the spacer material layer 415 over the hardmask layer 405 will be described. Method 800 may be utilized to perform the over etch process. Prior to operations of method 800, the processed structure 400 as shown in FIG. 4D may be obtained utilizing operations 305-330 of method 300 or operations 505-530 of method 500. Method 800 may then be initiated by forming a bias plasma from a halogen and carbon-containing precursor, such as a fluorine and carbon-containing precursor, at operation 805 in the processing region of the processing chamber where the processed structure 400 may be housed. At operation 810, the plasma effluents 910 of the fluorine and carbon-containing precursor may be directed by the plasma bias towards the processed structure 400, as illustrated in FIG. 9A. At operation 815, the plasma effluents 910 may selectively remove the remaining spacer material layer 415 overlaying the mandrels 410 and portions of the hardmask layer 405 relative to the exposed portions of the hardmask layer 405.

Without intending to be bound by any particular theory, the plasma effluents 910 produced from the fluorine and carbon-containing precursors may react with the spacer material layer 415, which may include silicon oxide, to form volatile byproducts, such as carbon oxide and silicon tetrafluoride. Due to the lack of oxygen in the hardmask layer 405, which may include silicon nitride or titanium nitride, instead of forming carbon oxide, a layer of carbon 920 may be deposited at the exposed portions of the hardmask layer 405. Accordingly, the processed structure 400 shown in FIG. 9B may be obtained through method 800 with the spacer material layer 415 selectively removed by the fluorine and carbon-containing precursor and the hardmask layer 405 protected by the carbon deposition 920 with substantial no or little removal. Following a subsequent carbon removal operation, the processed structure 400 shown in FIG. 9C may be obtained. Depending on the operating conditions, an etching selectivity of the spacer material layer 415 over the hardmask layer 405 by the fluorine and carbon-containing precursor of at least above or about 5:1, above or about 6:1, above or about 7:1, above or about 8:1, above or about 9:1, above or about 10:1, or greater may be achieved.

The bias plasma power forming the fluorine and carbon-containing plasma effluents may be between about 5 W and about 100 W. In some embodiments, the plasma power may be below or about 100 W, below or about 80 W, below or about 60 W, below or about 50 W, below or about 40 W, below or about 30 W, below or about 20 W, below or about 10 W, below or about 5 W, or lower. Relatively low bias power, such as below or about 20 W, may be utilized in method 800 to achieve sufficient dissociation of the fluorine and carbon-containing precursor while limiting undesired modification or removal of the hardmask layer 405 due to bombardment.

The fluorine and carbon-containing precursor may include fluorocarbon precursors. In some embodiments, the fluorine and carbon-containing precursor may include octafluorocyclobutane (C₄F₈). The fluorine and carbon-containing precursor may be flowed at a flow rate below or about 20 sccm, below or about 15 sccm, below or about 10 sccm, below or about 5 sccm, or lower. Given relatively low flow rates of the fluorine-containing precursor, a dilution gas may be flowed together with the fluorine and carbon-containing precursor to ensure uniform distribution of the fluorine and carbon-containing plasma effluents towards the processed structure 400. The dilution gas may include helium or other inert gases that may be flowed at a flow rate above or about 100 sccm, above or about 200 sccm, above or about 300 sccm, above or about 400 sccm, above or about 500 sccm, above or about 600 sccm, above or about 800 sccm, above or about 1,000 sccm, or higher. In some embodiments, the ratio of the flow rate of the dilution gas to the flow rate of the fluorine and carbon-containing precursor may be 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 150:1, 200:1, or greater. In some embodiments, the flow rate of the fluorine and carbon-containing precursor may be about 5 sccm, and the flow rate of the dilution gas, such as helium, may be about 400 sccm.

A relatively low pressure of the processing region may be maintained so as to increase the directionality of the removal of the spacer material layer 415. In some embodiments, the pressure may be maintained below or about 100 mTorr, below or about 50 mTorr, below or about 40 mTorr, below or about 30 mTorr, below or about 20 mTorr, below or about 10 mTorr, below or about 5 mTorr, below or about 1 mTorr, or lower. The temperature of the processed structure 400 or the processing region may be maintained at above or about 50° C., above or about 60° C., above or about 70° C., above or about 80° C., above or about 90° C., above or about 100° C., above or about 110° C., above or about 120° C., above or about 130° C., above or about 140° C., or above or about 150° C., or higher. In some embodiments, the temperature of the processed structure 400 or the processing region may be maintained at between about 80° C. and about 110° C., such as 100° C. Depending on the particular application, the selective etching of the spacer material layer 415 may last less than or about 60 seconds, less than or about 50 seconds, less than or about 45 seconds, less than or about 40 seconds, less than or about 35 seconds, less than or about 30 seconds, less than or about 25 seconds, less than or about 20 seconds, less than or about 15 seconds, less than or about 10 seconds, less than or about 5 seconds, or less in embodiments.

In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.

Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present technology. Accordingly, the above description should not be taken as limiting the scope of the technology.

Where a range of values is provided, it is understood that each intervening value, to the smallest fraction of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Any narrower range between any stated values or unstated intervening values in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of those smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a layer” includes a plurality of such layers, and reference to “the precursor” includes reference to one or more precursors and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”, “include(s)”, and “including”, when used in this specification and in the following claims, are intended to specify the presence of stated features, integers, components, or operations, but they do not preclude the presence or addition of one or more other features, integers, components, operations, acts, or groups. 

The invention claimed is:
 1. An etching method comprising: forming a treatment gas plasma within a processing region of a semiconductor processing chamber; modifying a surface of a first material on a semiconductor substrate within the processing region of the semiconductor processing chamber with effluents of the treatment gas plasma; modifying a surface of a second material on the semiconductor substrate with the effluents of the treatment gas plasma; forming a remote plasma from a fluorine-containing precursor to produce fluorine-containing plasma effluents; flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber; flowing water vapor to the processing region of the semiconductor processing chamber; and selectively removing the modified surface of the first material from the semiconductor substrate.
 2. The etching method of claim 1, wherein a temperature of the semiconductor substrate is maintained between about 5° C. and about 35° C.
 3. The etching method of claim 1, wherein the fluorine-containing plasma effluents are formed in a remote region of the semiconductor processing chamber fluidly coupled with, and physically separated from, the processing region of the semiconductor processing chamber.
 4. The etching method of claim 1, wherein the fluorine-containing plasma effluents are produced by a capacitively-coupled plasma at a power level of less than or about 300 W.
 5. The etching method of claim 1, wherein the first material comprises a spacer material including an oxide material, the second material comprises a hardmask material including a nitride material.
 6. The etching method of claim 1, wherein the etching method has a selectivity of at least 7:1 of the modified first material relative to the modified second material.
 7. An etching method comprising: forming a treatment gas plasma within a processing region of a semiconductor processing chamber; modifying a surface of a first material on a semiconductor substrate within the processing region of the semiconductor processing chamber with effluents of the treatment gas plasma, wherein the semiconductor substrate further comprises a second material different from the first material; forming a remote plasma from a fluorine-containing precursor to produce fluorine-containing plasma effluents; flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber; flowing water vapor to the processing region of the semiconductor processing chamber; and selectively removing the modified surface of the first material from the semiconductor substrate.
 8. The etching method of claim 7, further comprising modifying a surface of the second material on the semiconductor substrate with the effluents of the treatment gas plasma.
 9. The etching method of claim 7, further comprising adsorbing the water vapor at the surface of the first material.
 10. The etching method of claim 7, wherein a temperature of the semiconductor substrate is maintained between about 5° C. and about 35° C.
 11. The etching method of claim 7, wherein the fluorine-containing plasma effluents are formed in a remote region of the semiconductor processing chamber fluidly coupled with, and physically separated from, the processing region of the semiconductor processing chamber.
 12. The etching method of claim 7, wherein the first material comprises a spacer material including an oxide material, the second material comprises a hardmask material including a nitride material.
 13. The etching method of claim 7, wherein the etching method has a selectivity of at least 7:1 of the modified first material relative to the modified second material.
 14. An etching method comprising: forming a treatment gas plasma within a processing region of a semiconductor processing chamber; modifying a surface of a first material on a semiconductor substrate within the processing region of the semiconductor processing chamber with effluents of the treatment gas plasma; modifying a surface of a second material on the semiconductor substrate with the effluents of the treatment gas plasma; forming a remote plasma from a fluorine-containing precursor to produce fluorine-containing plasma effluents; flowing the fluorine-containing plasma effluents to the processing region of the semiconductor processing chamber; flowing water vapor to the processing region of the semiconductor processing chamber to combine with the fluorine-containing plasma effluents; and selectively removing the modified surface of the first material from the semiconductor substrate.
 15. The etching method of claim 14, wherein a temperature of the semiconductor substrate is maintained between about 0° C. and about 50° C.
 16. The etching method of claim 14, wherein the fluorine-containing plasma effluents are formed in a remote region of the semiconductor processing chamber fluidly coupled with, and physically separated from, the processing region of the semiconductor processing chamber.
 17. The etching method of claim 16, wherein the water vapor bypasses the remote plasma region of the semiconductor processing chamber when flowed to the processing region of the semiconductor processing chamber.
 18. The etching method of claim 14, wherein the fluorine-containing plasma effluents are produced by a capacitively-coupled plasma at a power level of less than or about 500 W.
 19. The etching method of claim 14, wherein the first material comprises a spacer material including an oxide material, the second material comprises a hardmask material including a nitride material.
 20. The etching method of claim 14, wherein the etching method has a selectivity of at least 5:1 of the modified first material relative to the modified second material. 